Delete the trash

How can i empty the trash folders in apple mail, have gone into mailbox and clicked erase deleted items, still there tried cmd,shift,back space and its still there. I have gone into web interface of iCloud and the trash folder is empty, but the one in apple mail is only deleting messages over three months old, how can i empty these folders one has over a hundred and odd mails in it.

No idea if it will have any effect but have you tried (with the trash mailbox selected) Mailbox => Rebuild?

Highlight the trash folder then delete mail on right hand side.

Select your Trash Folder and then move to the 'gear wheel' top right, highlight and select Empty Trash.

Thanks everyone.